National outbreak of Salmonella serotype saintpaul infections: importance of Texas restaurant investigations in implicating jalapeño peppers.
ABSTRACT In May 2008, PulseNet detected a multistate outbreak of Salmonella enterica serotype Saintpaul infections. Initial investigations identified an epidemiologic association between illness and consumption of raw tomatoes, yet cases continued. In mid-June, we investigated two clusters of outbreak strain infections in Texas among patrons of Restaurant A and two establishments of Restaurant Chain B to determine the outbreak's source.
We conducted independent case-control studies of Restaurant A and B patrons. Patients were matched to well controls by meal date. We conducted restaurant environmental investigations and traced the origin of implicated products. Forty-seven case-patients and 40 controls were enrolled in the Restaurant A study. Thirty case-patients and 31 controls were enrolled in the Restaurant Chain B study. In both studies, illness was independently associated with only one menu item, fresh salsa (Restaurant A: matched odds ratio [mOR], 37; 95% confidence interval [CI], 7.2-386; Restaurant B: mOR, 13; 95% CI 1.3-infinity). The only ingredient in common between the two salsas was raw jalapeño peppers. Cultures of jalapeño peppers collected from an importer that supplied Restaurant Chain B and serrano peppers and irrigation water from a Mexican farm that supplied that importer with jalapeño and serrano peppers grew the outbreak strain.
Jalapeño peppers, contaminated before arrival at the restaurants and served in uncooked fresh salsas, were the source of these infections. Our investigations, critical in understanding the broader multistate outbreak, exemplify an effective approach to investigating large foodborne outbreaks. Additional measures are needed to reduce produce contamination.
- SourceAvailable from: Francisco M. Ochoa Corona[Show abstract] [Hide abstract]
ABSTRACT: Although most plant diseases are the result of natural or unintentional causes, cropping systems and essential natural plant resources such as forests and grasslands also are considered vulnerable to actions of nefarious intent. Microbial forensics is defined as the application of scientific approaches to solving a crime that involves a microorganism; its goal is to investigate and present unbiased scientific evidence useful for attributing the crime to a perpetrator. Recent programs intended to enhance general capabilities in microbial forensics have included specific attention to plant pathogens. Compared to the strategies employed by traditional plant disease diagnosticians, forensic applications of plant pathogen diagnostics require unusually high levels of stringency, reliability, and prior vali-dation. These assays must be paired with court-defensible sampling methods, chain of custody, and other traditional and non-traditional methods of forensic investigation., © Springer Science+Business Media Dordrecht 2014 103 Forensics and Plant Pathology – Synergy of Two Disciplines Forensic plant pathology is a blend of the disciplines of plant pathology and forensic science that supports the investigation of plant diseases and pathogens by providing unbiased scientific methodology and evidence for criminal attribution. Important to this effort are traceback strategies for determining pathogen origin and movement pathway(s) as well as the possible role of human intent. Plant pathology and forensic science find a common arena with other disciplines within the realm of agricultural biosecurity, which includes science-based policies, measures and reg-ulatory frameworks for reacting to and managing risks associated with food, agriculture, forestry, and the environmental (UN 2002). The concept also includes other areas of environmental risk such as aquatic systems, and strongly associated sectors such as human health, justice and defense (Ochoa-Corona 2011). Unwanted movement of plant pathogens and pests into the agricultural sector can take place by various means including wind, water, insects, international commerce and travel. Such movement occurs frequently as inadvertent introduction of exotic pathogens and pests; however smuggling and illegal trade are examples of relevant criminal activities. In such situations multidisciplinary teams including representatives of the diagnostic, regulatory, and law enforcement communities must work in coor-dination to achieve the most effective response (Fig. 1). More creative strategies for both vertical and horizontal communication among the involved biosecurity and law enforcement agencies are needed (Ochoa-Corona 2011).Detection and Diagnostics of Plant Pathogens. Series: Plant Pathology in the 21st Century, Vol. 5., 1st edited by Maria Lodovica Gullino, Peter J M Bonants, 01/2014: chapter 7: pages 103-115; Springer., ISBN: ISBN 978-94-017-9020-8 (eBook)
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ABSTRACT: This manuscript considers available evidence that a specific Salmonella strain could be used as an effective orally-administered option for cancer therapy involving the brain. It has been established that Salmonella preferentially colonizes neoplastic tissue and thrives as a facultative anaerobe in the intra-tumor environment. Although Salmonella accumulates in tumors by passive processes, it is still possible for lipopolysaccharide to cause sepsis and endotoxic shock during the migration of bacteria to the tumor site. An LPS-free version of a recently identified Salmonella isolate may have the capability to circumvent the blood brain barrier and provide a safer method of reaching brain tumors. This isolate merits further research as a “Trojan horse” for future oral biotherapy of brain cancer.Medical Hypotheses 09/2014; · 1.15 Impact Factor
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ABSTRACT: The popularity in the consumption of fresh and fresh-cut vegetables continues to increase globally. Fresh vegetables are an integral part of a healthy diet, providing vitamins, minerals, antioxidants and other health-promoting compounds. The diversity of fresh vegetables and packaging formats (spring mix in clamshell container, bagged heads of lettuce) support increased consumption. Unfortunately, vegetable production and processing practices are not sufficient to ensure complete microbial safety. This review highlights a few specific areas that require greater attention and research. Selected outbreaks are presented to emphasize the need for science-based ‘best practices’. Laboratory and field studies have focused on inactivation of pathogens associated with manure in liquid, slurry or solid forms. As production practices change, other forms and types of soil amendments are being used more prevalently. Information regarding the microbial safety of fish emulsion and pellet form of manure is limited. The topic of global climate change is controversial, but the potential effect on agriculture cannot be ignored. Changes in temperature, precipitation, humidity and wind can impact crops and the microorganisms that are associated with production environments. Climate change could potentially enhance the ability of pathogens to survive and persist in soil, water and crops, increasing human health risks. Limited research has focused on the prevalence and behaviour of viruses in pre and post-harvest environments and on vegetable commodities. Globally, viruses are a major cause of foodborne illnesses, but are seldom tested for in soil, soil amendments, manure and crops. Greater attention must also be given to the improvement in the microbial quality of seeds used in sprout production. Human pathogens associated with seeds can result in contamination of sprouts intended for human consumption, even when all appropriate ‘best practices’ are used by sprout growers.Microbial Biotechnology 10/2014; · 3.21 Impact Factor
National Outbreak of Salmonella Serotype Saintpaul
Infections: Importance of Texas Restaurant
Investigations in Implicating Jalapen ˜o Peppers
Rajal K. Mody1,2*, Sharon A. Greene2, Linda Gaul3, Adrianne Sever1, Sarah Pichette4, Ingrid Zambrana4,
Thi Dang3, Angie Gass5, Rene ´ Wood5, Karen Herman2, Laura B. Cantwell2, Gerhard Falkenhorst2,
Kathleen Wannemuehler2, Robert M. Hoekstra2, Isaac McCullum2, Amy Cone5, Lou Franklin5, Jana
Austin2, Kristin Delea6, Casey Barton Behravesh2, Samir V. Sodha2, J. Christopher Yee4, Brian Emanuel4,
Sufian F. Al-Khaldi4, Val Jefferson4, Ian T. Williams2, Patricia M. Griffin2, David L. Swerdlow2
1Scientific Education and Professional Development Program Office, Epidemic Intelligence Service, Centers for Disease Control and Prevention, Atlanta, Georgia, United
States of America, 2Division of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease
Control and Prevention, Atlanta, Georgia, United States of America, 3Texas Department of State Health Services, Austin, Texas, United States of America, 4United States
Food and Drug Administration, Silver Spring, Maryland, United States of America, 5Wichita Falls-Wichita County Public Health District, Wichita Falls, Texas, United States
of America, 6National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America
Background: In May 2008, PulseNet detected a multistate outbreak of Salmonella enterica serotype Saintpaul infections.
Initial investigations identified an epidemiologic association between illness and consumption of raw tomatoes, yet cases
continued. In mid-June, we investigated two clusters of outbreak strain infections in Texas among patrons of Restaurant A
and two establishments of Restaurant Chain B to determine the outbreak’s source.
Methodology/Principal Findings: We conducted independent case-control studies of Restaurant A and B patrons. Patients
were matched to well controls by meal date. We conducted restaurant environmental investigations and traced the origin
of implicated products. Forty-seven case-patients and 40 controls were enrolled in the Restaurant A study. Thirty case-
patients and 31 controls were enrolled in the Restaurant Chain B study. In both studies, illness was independently
associated with only one menu item, fresh salsa (Restaurant A: matched odds ratio [mOR], 37; 95% confidence interval [CI],
7.2–386; Restaurant B: mOR, 13; 95% CI 1.3–infinity). The only ingredient in common between the two salsas was raw
jalapen ˜o peppers. Cultures of jalapen ˜o peppers collected from an importer that supplied Restaurant Chain B and serrano
peppers and irrigation water from a Mexican farm that supplied that importer with jalapen ˜o and serrano peppers grew the
Conclusions/Significance: Jalapen ˜o peppers, contaminated before arrival at the restaurants and served in uncooked fresh
salsas, were the source of these infections. Our investigations, critical in understanding the broader multistate outbreak,
exemplify an effective approach to investigating large foodborne outbreaks. Additional measures are needed to reduce
Citation: Mody RK, Greene SA, Gaul L, Sever A, Pichette S, et al. (2011) National Outbreak of Salmonella Serotype Saintpaul Infections: Importance of Texas
Restaurant Investigations in Implicating Jalapen ˜o Peppers. PLoS ONE 6(2): e16579. doi:10.1371/journal.pone.0016579
Editor: Qamaruddin Nizami, Aga Khan University, Pakistan
Received November 4, 2010; Accepted January 5, 2011; Published February 23, 2011
This is an open-access article distributed under the terms of the Creative Commons Public Domain declaration which stipulates that, once placed in the public
domain, this work may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose.
Funding: This work was supported by core government funding. The funders had no role in study design, data collection and analysis, decision to publish, or
preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
* E-mail: email@example.com
Long-distance transportation keeps stores and restaurants
stocked with a wide assortment of fresh fruits and vegetables year
round. However, with this abundance has come increased risk of
large produce-associated foodborne outbreaks [1–3]. Among
produce-associated outbreaks with known etiologic agents, the
most common pathogen is non-typhoidal Salmonella, a diverse
group of bacteria that live in intestinal tracts of many animals and
survive in environments from the farm to the table [3,4]. The
overall incidence of Salmonella infection from all sources in 2009
was more than double the national target for 2010; little progress
towards this goal has been observed since 1996 .
In May 2008, a multistate outbreak of Salmonella enterica serotype
Saintpaul infections with indistinguishable pulsed-field gel elec-
trophoresis (PFGE) patterns was detected which ultimately
became the largest known foodborne outbreak in the United
States in over 10 years. Initial investigations identified an
association between illness and the consumption of raw tomatoes
. On June 7, the US Food and Drug Administration (FDA)
issued a national alert to avoid ‘‘raw red plum, red Roma, and red
round tomatoes’’ .
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epidemiologically implicated and the sources of suspected tomatoes
were not converging to any specific growing region or to a common
distributor. Furthermore, a possible association between infections and
eating Mexican-style foods began to emerge. Because tomatoes are a
staple ingredient in many cuisines, not just Mexican, this finding
suggested there might be something else, besides tomatoes, more
unique to Mexican food involved. Collectively, these observations
raised concern that an unidentified vehicle of infection might exist.
In mid-June, a cluster of cases was identified among persons
who ate at Restaurant A, a Mexican-style restaurant in Wichita
Falls, Texas, providing an opportunity for evaluation of the
discrete list of foods served. A second cluster of cases was
subsequently identified among persons who ate at two locations of
Mexican-style Restaurant Chain B, in northern Texas. Here we
describe the investigation of cases associated with Restaurant A
and Restaurant Chain B conducted to further characterize the
source of infections in the broader multistate outbreak.
The National Center for Emerging and Zoonotic Infectious
Diseases within the Centers for Disease Control and Prevention
determined that these investigations did not meet the definition of
research as provided by 45 CFR4 6.102(d) and therefore IRB
review was not required. The basis for this determination was that
the primary purpose of this activity was to identify, characterize,
and control disease in response to an immediate public health
threat. All participants were explained the purpose of the
investigation and participation was voluntary.
We defined confirmed cases as culture-confirmed Salmonella
infections reported to the Texas Department of State Health
Services (TXDSHS) or Wichita Falls-Wichita County Public
Health District (WFWCPHD) during June 2008 in persons who
ate food from Restaurant A or from either of two Restaurant
Chain B establishments during the seven days before diarrhea
began. We defined probable cases as $3 loose stools in a 24-hour
period starting within 7 days after eating at Restaurant A or at
either Restaurant Chain B location.
We obtained lists of culture-confirmed Salmonella infections in
each of the three counties where the three restaurants were
located. Outbreak strain infections, defined as Salmonella enterica
serotype Saintpaul with XbaI PFGE pattern JN6X01.0048, were
detected through routine laboratory-based surveillance, whereby
clinical laboratories forward Salmonella isolates to public health
laboratories for serotyping, PFGE analysis, and reporting .
Additional culture-confirmed Salmonella infections for which
subtyping analyses were not performed were detected through
mandated Salmonella case-based reporting by physicians.
We then determined which infections occurred in persons who
had consumed food from Restaurant A or from either Restaurant
Chain B establishment during the 7 days before diarrhea began
through telephone interviews. These confirmed case-patients were
asked to provide names and telephone numbers of their meal
companions. Probable case-patients were identified from this list of
meal companions. Several probable case-patients with resolved
gastroenteritis submitted rectal swabs for culture at the TXDSHS
laboratory during our investigation to more accurately classify
Beginning June 21, we conducted sequential, independent,
matched case-control studies of Restaurant A and Restaurant
Chain B patrons. Well meal companions, defined as persons who
ate meals at either Restaurant A or B with confirmed case-patients
but who did not develop diarrhea, abdominal cramping, fever, or
vomiting during the 7 days following the meal, were enrolled as
controls. Trained interviewers administered standardized ques-
tionnaires developed to measure exposure to all menu items.
Because patrons could modify menu items by asking that standard
ingredients or condiments be excluded or by adding non-standard
ingredients or condiments, respondents were systematically
questioned about any modifications made. In addition to assessing
exposures to menu items, we obtained recipes for each item, to
assess exposures to specific ingredients.
Data from each case-control study were separately analyzed
using SAS 9.2 (SAS Institute, Cary, NC). We used exact
conditional logistic regression to obtain matched odds ratios and
95% confidence intervals for the association between illness and
each menu item and ingredient. Because both gender and age are
often associated with diet preferences, we also calculated sex- and
age group- (,10 and $10 years) adjusted estimates. We used a p-
value threshold of #0.05 for significance and did not adjust for
multiple comparisons. Not all case-patients had consumed their
meals with controls. Therefore, to include as many case-patients as
possible in the analyses, we matched case-patients to controls by
meal date. We allowed a variable ratio of controls to cases in each
matched set. Sex- and age group-adjusted multivariate models
were constructed when two or more menu items or ingredients
were associated with illness in univariate analysis. To maximize
our sensitivity to detect an association between raw tomato
consumption and illness, all menu items that regularly contained
raw tomatoes were treated as containing them even if the
restaurant reportedly stopped using raw tomatoes in response to
initial outbreak alerts.
Restaurant environmental investigations
Environmental investigations of the restaurants included review
of food storage and preparation, inquiries into worker absenteeism
and illness, and collection of environmental and food samples for
testing using the FDA’s Bacteriological Analytical Manual (BAM)
Salmonella culture method at TXDSHS and WFWCPHD labora-
The FDA and Centers for Disease Control and Prevention
(CDC) formed a joint team in July 2008 to trace the path of
implicated product from both Restaurant A and Restaurant Chain
B back to the farm. We used dates of patient exposures to the
restaurants as the starting point to identify suspect shipments.
Distribution records, including invoices and bills of lading, were
used to determine shipment and receipt dates at each point in the
supply chain. FDA investigators collected product and environ-
mental samples for testing using the BAM method at FDA
Restaurant A epidemiological investigation
Thirty-two culture-confirmed outbreak strain
or non-subtyped Salmonella infections were identified during June
2008 in Wichita County. Of 30 patients who could be contacted,
Restaurant Investigations in Salmonella Outbreak
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29 (97%), met the confirmed case definition and consumed food
from Restaurant A. In addition, 25 probable case-patients were
identified; three submitted rectal swabs and were reclassified as
confirmed case-patients following isolation of the outbreak strain.
All patients dined at Restaurant A from May 30 through June 2.
We enrolled 47 case-patients (25
confirmed, 22 probable). Of the 25 confirmed case-patients, 19
had outbreak strain infections; Salmonella isolates from the other six
were not sent to the TXDSHS laboratory for serotyping or
subtyping. We enrolled 40 meal date-matched controls.
Among enrolled case-patients, dates of dining at Restaurant A
and dates of diarrhea onset were similar for culture-confirmed and
probable cases (Figure 1). The median incubation period was 2 days
for both culture-confirmed (range, ,1–7 days) and probable (range,
1–5 days) cases. Case-patients ranged in age from 2 to 63 years; 51
percent were female, four (9%) were hospitalized, and none died.
Of 244 menu items individually evaluated, only red salsa and
cheese sauce were statistically associated with illness. Red salsa was
consumed by 45 (96%) case-patients and 11 (28%) controls
(matched odds ratio [mOR], 47; 95% confidence interval [CI],
9.9–456). Cheese sauce was consumed by 43 (91%) case-patients
and 28 (70%) controls (mOR, 4.4; 95% CI, 1.2–21) (Table 1). In a
multivariate model containing red salsa and cheese sauce as
independent exposure variables, only red salsa was independently
associated with illness (adjusted-mOR, 37; 95% CI, 7.2–386)
(Table 2). Of ingredients individually evaluated, consumption of
raw jalapen ˜o peppers and raw tomatoes as ingredients in any dish
were statistically associated with illness. Forty-five (96%) case-
patients and 16 (40%) controls ate raw jalapen ˜o peppers (mOR, 28;
95% CI, 6.1–267). Forty-six (98%) case-patients and 29 (73%)
controls ate raw tomatoes (mOR, 18; 95% CI, 2.3–833) (Table 1).
In a multivariate model containing raw tomatoes and raw jalapen ˜o
peppers as independent exposure variables, only raw jalapen ˜o
peppers were independently associated with illness (adjusted-mOR,
25; 95% CI, 3.4–.1000) (Table 2). Adjustment for age and sex did
not alter findings of the Restaurant A case-control study (Table 1).
Restaurant chain B epidemiological investigation
Thirty-three culture-confirmed outbreak strain
or non-subtyped Salmonella infections were identified through
routine surveillance during June 2008 in the two counties in which
the Restaurant Chain B establishments were located. Of 32
patients who could be contacted, 23 (72%) met the confirmed case
definition and consumed food from either of the two Restaurant
Chain B establishments. In addition, nine probable case-patients
were identified. All patients dined at Restaurant Chain B from
May 23 through June 12, with only two exposures before June 2.
We enrolled 30 case-patients (21
confirmed, 9 probable). Of the 21 confirmed case-patients, 13
had outbreak strain infections; Salmonella isolates from the other
eight were not sent to the TXDSHS laboratory for serotyping or
subtyping. We enrolled 30 meal date-matched controls. Matched
controls could not be found for nine (5 confirmed, 4 probable)
case-patients, leaving only 21 case-patients included in the
matched analyses (Figure 2).
Among enrolled case-patients, dates of dining at Restaurant
Chain B and dates of diarrhea onset were similar for culture-
confirmed and probable cases (Figure 2). The median incubation
period was 3 days for both culture-confirmed (range, 1–7 days)
and probable (range, 1–5 days) cases. Case-patients ranged in age
from 5 to 76 years; 47 percent were female, nine (30%) were
hospitalized, and none died.
Figure 1. Restaurant A-associated cases by date of meal (top) and diarrhea onset (bottom). Black bars represent 25 confirmed cases. Grey
bars represent 22 probable cases. The exact dates of diarrhea onset are not available for 4 probable cases.
Restaurant Investigations in Salmonella Outbreak
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Of 101 menu items individually evaluated, no items were
significantly associated with illness in the absence of adjustment for
possible confounders. With adjustment for age and sex, only red
salsa was statistically associated with illness, consumed by all 21
case-patients and 24 (77%) controls (adjusted-mOR, 13; 95% CI,
1.3–infinity) (Table 1). No ingredients were significantly associated
with illness in the absence of adjustment for possible confounders.
With adjustment for age and sex, the only ingredient in Restaurant
Chain B dishes associated with illness was raw jalapen ˜o peppers,
consumed by all 21 case-patients and 25 (81%) controls (adjusted-
mOR, 13; 95% CI: 1.3–infinity) (Table 1). All nine case-patients
excluded for lack of meal date-matched controls consumed red
salsa and raw jalapen ˜o peppers at the restaurants.
The Restaurant A salsa contained raw Roma or red round
tomatoes, raw jalapen ˜o peppers, salt, granulated garlic, and red
pepper flakes. During the 4 day period in which case-patients ate
at Restaurant A, approximately 25 25-pound (11.3 kg) boxes of
tomatoes of various brands were used by the restaurant, whereas
only one box of jalapen ˜o peppers was likely used.
The recipe for Restaurant Chain B salsa was similar to
Restaurant A’s, except that it always used commercially canned
tomatoes, not raw tomatoes. Restaurant A and Restaurant Chain
B used different brands of salt, granulated garlic, and red pepper
flakes. Therefore, the only ingredient that might have been in
common between the two salsas was raw jalapen ˜o peppers. The
Table 1. Consumption of selected food items by case-patients and controls by restaurant cluster.a
Patients Controls Matched Odds RatioAdjusted Matched Odds Ratiob
Restaurant A(N=47) (N=40) (95% CI)(95% CI)
Menu item consumed no (%)
Red salsa 45(96)11(28) 47 (9.9–456)c
Cheese sauce43 (91)28(70) 4.4 (1.2–21)c
Tortilla chips41(87)33(83) 1.4 (0.4–5.4)1.4 (0.4–5.5)
Guacamole30 (64) 21 (53)1.7 (0.6–4.6)1.6 (0.6–4.5)
Fajitas20(43) 23 (58)0.4(0.1–1.4)0.3(0.1–1.4)
Ingredient consumed no (%)
Raw tomatoes46 (98)29(73) 18 (2.3–833)c
Raw jalapen ˜o peppers45(96) 16(40) 28(6.1–267)c
Avocados30(64) 21(53) 1.7 (0.6–4.6)1.6(0.6–4.5)
Restaurant Chain B(N=21) (N=31)
Menu item consumed no (%)
Red salsa 21(100) 24(77)8.1d
Ingredient consumedno (%)
Raw jalapen ˜o peppers21(100)25(81) 7.7d
Raw tomatoes 15(71) 16(52) 1.7(0.4–7.8) 1.7(0.4–8.7)
aExposures reported by at least 40 percent of case-patients are shown.
bAdjusted for sex and age group (,10 versus $10 years old).
dMedian unbiased estimate.
Table 2. Multivariate assessment of associations of menu items and ingredients with illness among Restaurant A patrons.
PatientsControls Adjusted Matched Odds Ratioa
Restaurant A (N=47)(N=40) (95% CI)
Menu Item consumedb
Red salsa 45(96) 11(28) 37(7.2–386)c
Cheese sauce43(91) 28(70)0.9(0.1–8.5)
Raw jalapen ˜o peppers45(96)16 (40)25(3.4–.1000)c
aAdjusted for sex and age group (,10 versus $10 years old).
bRed salsa and cheese sauce are the two exposure variables in the menu item model.
dRaw tomatoes and raw jalapen ˜o peppers are the two exposure variables in the ingredient model.
Restaurant Investigations in Salmonella Outbreak
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dry spices were purchased in bulk, lasting longer than the observed
The implicated salsas were made in large batches. Individual
servings were placed on multiple trays stacked above a single layer
of ice in the service lines. The restaurants did not routinely
measure the temperature of the salsa on these trays.
The restaurant managers denied any food worker illness or
absenteeism during the case-patients’ exposure periods. Cultures
of food and environmental samples, including tomatoes, jalapen ˜o
peppers, salsa, spices, and swabs of food processing and storage
surfaces collected from Restaurant A and one Restaurant Chain B
location did not yield serotype Saintpaul. However, no foods
served during the dates of exposure were available for testing.
Jalapen ˜o peppers used in Restaurant A during the period of
case-patient exposure were traced to Importer A in southern
Texas. Jalapen ˜o peppers used in the Restaurant Chain B
restaurants during the period of case-patient exposure were traced
to Importer B, located near Importer A. This area of Texas is
home to many produce import firms. During our record review we
directly observed that these firms commonly trade goods amongst
themselves to fill orders.
Culture of a jalapen ˜o pepper sample collected from Importer B
on July 11 yielded the outbreak strain. These peppers were traced
to a packing facility in Nuevo Leon, Mexico. The traceback from
the packing facility was complex with commingling of product and
a network of interrelated distribution points. FDA investigations
continued on two Mexican farms (Farm A and Farm B) that were
major suppliers of peppers to the packing facility, though records
indicate that other farms also supplied the packing facility during
this time period. Farm A grew Roma tomatoes in addition to
jalapen ˜o and serrano peppers. Environmental sampling at Farm A
identified Salmonella, but none that were serotype Saintpaul. Farm
B, located approximately 100 miles from Farm A, was the packing
facility’s main pepper supplier. It grew jalapen ˜o peppers and
serrano peppers, but not tomatoes, and harvested produce from
mid-April to mid-June (Figure 3). The outbreak strain was isolated
from two samples taken from Farm B—agricultural water and
serrano peppers found in the field.
In the midst of a massive multistate outbreak of Salmonella
serotype Saintpaul infections, investigation of two clusters of cases
among patrons of restaurants in Texas provided evidence
implicating jalapen ˜o peppers. First, the only ingredient in the
restaurants independently associated with illness was raw jalapen ˜o
peppers. Second, the only ingredient in common between the two
restaurant salsa recipes was raw jalapen ˜o peppers. Third, the
outbreak strain was isolated from serrano peppers and irrigation
water on a farm that grew epidemiologically implicated jalapen ˜o
peppers. Harvesting of peppers from the farm began shortly before
the first cases of the multistate outbreak and continued for a
duration that could account for the entire outbreak. Although, to
our knowledge, no reports of Salmonella infections acquired from
consumption of jalapen ˜o peppers existed before our investigations,
it was known that Salmonella grows well in extracts of homogenized
jalapen ˜o peppers .
Figure 2. Restaurant B-associated cases by date of meal (top) and diarrhea onset (bottom). Solid black bars represent 16 confirmed cases
with meal date-matched controls. Solid grey bars represent 5 probable cases with meal date-matched controls. The dashed black and grey bars
represent 5 confirmed and 4 probable cases, respectively, that were not included in the matched analyses because they had no meal date-matched
Restaurant Investigations in Salmonella Outbreak
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This outbreak is one in a series of increasingly recognized, large,
and widely-dispersed outbreaks caused by contaminated produce
[10–17]. The proportion of all reported foodborne outbreaks in
the United States associated with contaminated produce increased
from 0.7% in the 1970s to 6% in the 1990s; this trend appears to
be ongoing [2,3]. Related forces likely driving this shift include
increasing consumption of fresh produce, increasing centralization
of the produce industry to maintain year-round availability,
expansion of growing fields to areas adjacent to animal production
areas, and improved detection and investigation of widely
dispersed outbreaks [1,2,18]. Centralization might foster outbreaks
by increasing the number of points at which contamination may
occur and the amount of product that could be contaminated in a
given event. Centralization could also lead to more widely
dispersed outbreaks because contaminated produce may be widely
Routine laboratory-based surveillance, especially molecular
subtyping by PulseNet USA, has greatly improved our ability to
detect widely dispersed outbreaks . However, investigation of
these outbreaks can be challenging when there is little apparent
epidemiologic clustering by person, place, or time, and because of
time delays inherent with laboratory-based surveillance. When
generating hypotheses, investigators must consider an enormous
list of possible food, water, animal, and environmental exposures
. Furthermore, patients are often interviewed several weeks
after becoming ill, when recall of basic foods consumed is limited,
and even more diminished for specific details, such as tomato type
or ingredients within prepared dishes.
Our investigations highlight how these challenges can be reduced
by searching for and investigating clusters of cases associated with
specific food establishments or events within a larger outbreak.
Investigations of localized clusters simplify hypothesis generation
because the suspected sources of infection are usually limited to a
finite list of menu items . Likewise, patient recall is enhanced by
focusing on a specific, often memorable, meal. Furthermore,
investigators can obtain recipes to assess associations between
illnessand specific ingredients; thisis especially helpful in identifying
stealthy vehicles, such as jalapen ˜o peppers, that some people might
have been unaware they consumed. Additionally, turnover rate of
ingredients within restaurants can be evaluated to find those
ingredients that best fit the exposure period of patients in the
outbreak. For example, at Restaurant A we noted that approxi-
mately 25 boxesoftomatoeswould have been used duringthe4-day
period when patients ate there compared with one box of jalapeno
peppers; thus contamination present in just one box of peppers
could account for the Restaurant A outbreak duration. Finally, food
delivery invoices kept by restaurants and caterers contain specific
information that can improve the accuracy of traceback investiga-
tions; this is particularly important in fresh produce-associated
outbreaks because fruits and vegetables sold in stores typically come
in many varieties and may have minimal labeling to identify their
source. Collectively, these attributes of localized cluster investiga-
tions serve to generate more specific exposure information .
Detailed exposure information allowed us to document the
stealthy nature of jalapen ˜o peppers in this outbreak. Three case-
patients in our study of Restaurant Chain B also participated in a
multistate case-control study . Our study, aided by restaurant
recipes, documented that all three consumed foods containing raw
jalapen ˜o peppers at the restaurant, as all reported having consumed
salsa; one patient also reported adding raw jalapen ˜o peppers to an
entre ´e. In the multistate study, which asked patients to recall
consumption of specific ingredients in restaurants, the two patients,
whose only exposure to raw jalapen ˜o peppers at Restaurant Chain
B was from salsa, denied exposure to this ingredient, presumably
because they were unaware that it was present in the salsa.
Some restaurant-prepared fresh salsas might be prone to
amplifying and spreading small amounts of bacterial contamina-
tion present on a few individual produce items to a large number
of servings because they often are made in large batches
containing pooled and diced raw produce ingredients .
Salmonella grows better on diced, as compared with intact,
tomatoes and jalapen ˜o peppers . Diced tomatoes, and any
foods containing them, unless acidified to a pH of ,4.2, are
included in the 2009 FDA Food Code as a potentially hazardous
food, and thus require storage at or below 41uF (5uC) . High
Salmonella growth rates have been observed in salsas prepared
using the Restaurant A and Restaurant Chain B recipes at
temperatures at or above 54uF (12uC) . Growth might be
reduced by replacing granulated garlic with fresh garlic and
adding lime juice to the recipes .
Because so much produce is consumed raw and disinfection
methods are not highly effective on fresh produce, the keys to
Figure 3. Cases by date of onset in multistate outbreak and dates of pepper harvest. The blue bars represent 1500 cases in the multistate
outbreak of Salmonella Saintpaul infections reported from 43 states and the District of Columbia, and Canada; these data are modified from reference
6. The orange bar represents the period of serrano pepper harvest (April 18 through May 31) on the farm from which the outbreak strain was isolated.
The green bar represents the period of jalapen ˜o pepper harvest (April 14 through June 14) on the same farm. Jalapen ˜o and serrano peppers might
begin to wrinkle and lose quality as early as three weeks after harvest (indicated by dashed lines to the right of harvest periods), but refrigeration
might extend their shelf life well beyond three weeks (FDA, personal communication).
Restaurant Investigations in Salmonella Outbreak
PLoS ONE | www.plosone.org6February 2011 | Volume 6 | Issue 2 | e16579
preventing produce-associated outbreaks are preventing the initial
contamination and minimizing handling practices that lead to
amplification . Water used for irrigation and pesticide
application is one possible source of contamination in this
outbreak. Keeping water used for these purposes protected from
animals and waste run-off is important. Modifying salsa recipes to
include growth-inhibitory ingredients might limit amplification of
Salmonella ; all fresh salsas with a pH $4.2 should be stored in
adherence with established time and temperature recommenda-
tions to minimize growth . Additionally, because Salmonella
grows rapidly in diced jalapen ˜o peppers, regulatory consideration
is warranted to define foods containing them as potentially
During the summer of 2008, 1,500 Salmonella serotype Saintpaul
infections with the outbreak PFGE pattern were reported from 43
states and the District of Columbia and Canada. Shortly after
jalapen ˜o peppers were identified as the probable source of
infections in the two Texas clusters described in this report, an
independent investigation of restaurant-acquired serotype Saint-
paul infections in Minnesota implicated raw jalapen ˜o peppers .
During the outbreak, 33 restaurant clusters were reported
nationally; 31 served foods that contained jalapen ˜o or serrano
The Farm B chili pepper harvest period (April 14–June 14)
closely mirrors the range of illness onset dates in the multistate
outbreak (April 16–August 26) (CDC and FDA, unpublished data).
Chili peppers might begin to wrinkle and lose quality 3 weeks after
harvest, but refrigeration may extend their shelf life well beyond
this period (FDA, personal communication). Therefore, Farm B
peppers were harvested shortly before and available during this
multistate outbreak (Figure 3). On July 30, national alerts advised
persons to avoid raw jalapen ˜o and serrano peppers grown or
packed in Mexico. The two restaurant cluster investigations in
Texas reported here were critical in solving this complex multistate
Conceived and designed the experiments: RKM SAG LG AS SP IZ CBB
SFA-K VJ ITW PMG DLS. Performed the experiments: RKM SAG AS
SP IZ TD AG RW KH LBC GF AC LF JA KD CBB SVS JCY BE SFA-K
VJ DLS. Analyzed the data: RKM SAG AS SP IZ KW RMH IM SFA-K
VJ DLS. Wrote the paper: RKM PMG DLS. Revised manuscript for
important intellectual content: SAG LG AS SP IZ TD AG RW KH LBC
GH KW RMH IM AC LF JA KD CBB SVS JCY BE SFA VJ ITW PMG
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Restaurant Investigations in Salmonella Outbreak
PLoS ONE | www.plosone.org7February 2011 | Volume 6 | Issue 2 | e16579